Certain medical devices are inserted and/or implanted into the body of a patient. Examples of these devices include catheters, guidewires, medical balloons, stents, and stent-grafts. When a device is advanced through the body, its progress can be monitored, e.g., tracked, so that the device can be delivered properly to a target site. After the device is delivered to the target site, the device can be monitored to determine whether it has been placed properly and/or is functioning properly.
One method of monitoring a medical device is magnetic resonance imaging (MRI). MRI is a non-invasive technique that uses a magnetic field and radio waves to image the body. In some MRI procedures, the patient is exposed to a magnetic field, which interacts with certain atoms, e.g., hydrogen atoms, in the patient's body. Incident radio waves are then directed at the patient. The incident radio waves interact with atoms in the patient's body, and produce characteristic return radio waves. The return radio waves are detected by a scanner and processed by a computer to generate an image of the body.
In some MRI procedures, a contrast medium or agent is introduced into the body to enhance the visibility of an image. For example, the contrast agent can produce an area that is darker or lighter relative to other areas to enhance visibility. The contrast agent can alter the response of atoms near the contrast agent to the magnetic field. As a result, the interaction between the incident radio waves and the atoms can be altered, which consequently, can affect the return radio waves produced and the image generated.